The present invention relates to gas generating material, and particularly to a gas generating grain which is made of an azide based material that generates gas upon combustion and which has an ignition enhancing coating thereon.
Various sodium azide based materials are known for generating gas on combustion. These materials are used to inflate a vehicle occupant restraint such as an air bag. In the event of sudden deceleration of the vehicle, such as would be caused by a collision, the gas generating material is ignited and gas is generated. The gas is directed into the air bag to inflate the air bag. The air bag then cushions the movement of the occupant relative to the vehicle and prevents the occupant from having a violent collision with parts of the vehicle.
In air bag systems, the gas generating material desirably must be capable of producing nontoxic, nonflammable, and essentially smokeless gas over a wide variety of temperatures and other environmental conditions. The gases that are generated must be at a sufficiently low temperature so as not to destroy the restraint or injure the occupant. The gas generating material also must be capable of generating a substantial amount of gas within a very short period of time.
Known materials which generate gas to inflate an inflatable occupant restraint include an alkali metal azide. U.S. Pat. Nos. 4,062,708; 3,931,040 and 3,895,098 are examples of patents which disclose such materials for generating gas to inflate an air bag. U.S. Pat. No. 4,062,708 discloses a material which includes sodium azide and iron oxide. The material is formed into pellets. When the pellets burn, nitrogen gas is produced and some combustion products are left as a substantially solid sinter with sufficient interconnected cells and passages to hold combustion products which would undesirably enter the air bag.
In application Ser. No. 946,705, filed Dec. 24, 1986, now U.S. Pat. No. 4,698,107, issued Oct. 6, 1987, and assigned to the assignee of the present invention, a gas generating grain having an ignition enhancing coating thereon is disclosed. The ignition enhancing coating includes a fluoroelastomer as a binder. The fluoroelastomer when ignited creates some carbon monoxide which is undesirable.